SHGC and U-factor for Texas: what the numbers should look like

What are SHGC and U-factor, in plain words?

SHGC tells you how much sun heat a window lets in. U-factor tells you how fast heat leaks through it. Both are numbers on the NFRC label. For both, a lower number means less heat moves through the product.

The Department of Energy defines them this way. “SHGC is a measure of heat transmitted through glass and theoretically varies between 0 and 1, where the lower the number, the less heat is transmitted.” And “the U-factor is a measure of the rate of heat flow through glazing products; the lower a U-factor, the less heat will flow through the window.”

You can read more in the SHGC and U-factor glossary entries. For a walk through the label itself, see the NFRC label guide.

Which number matters more in North Texas?

In a hot climate, SHGC usually comes first. The Department of Energy says: “In warm climates, where air conditioning costs are the concern, buy or specify products with low SHGCs to reduce unwanted heat gain.” U-factor still matters, but sun load drives summer cost.

Think of a west-facing wall of glass at 4 p.m. in August. Sun pours in. A low-SHGC coating blocks much of that heat before it enters the room. A low U-factor then slows the heat that builds up on the glass surface and moves in.

Winter is the other season. North Texas gets cold nights, so U-factor keeps rooms comfortable near the glass. A good spec balances both. It also checks visible transmittance, so low SHGC glass does not make the room dark.

How does the climate zone set the target?

The climate zone sets which ENERGY STAR limits apply. ENERGY STAR says its criteria “vary for each of the climate zones shown in the map.” The Department of Energy tells buyers to find the zone first, then choose products at or below the limits.

ENERGY STAR publishes its window limits as tables. This guide does not copy a Texas number. Open the current ENERGY STAR page and the zone finder to read the exact figures for your county. Use the ENERGY STAR zone finder with your address or county to confirm your zone.

The ENERGY STAR climate zone entry explains zones in short form. Keep in mind that ENERGY STAR is a program target. Your city’s energy code is a separate legal rule.

What do local codes say?

Codes differ by city, and they change. As of November 2026, the Town of Highland Park residential builders packet lists a plan checklist line for “Window & Door Sizes w/SHGC & U-Factor” with the note “(SHGC < 0.25 max & U-Factor < 0.35 max)”. It also asks for “2024 IECC compliance signed by an energy consultant with ICC certification.”

That is one town’s checklist for plan submittals. It may not apply to every window swap. Confirm the scope with the Town of Highland Park before you order glass. The same goes for any other city.

Item	What the source says	Where it applies
ENERGY STAR criteria	Vary by climate zone	Program target, set by tables on the ENERGY STAR site
DOE advice for hot climates	Low SHGC; low gain is under 0.4	National guidance for buyers
Highland Park builders packet	SHGC under 0.25 max, U-factor under 0.35 max	Plan checklist for residential permits, as of November 2026
City energy code	Varies by city and code year	Confirm with your city’s permit office

Our Park Cities page lists the permit offices for Highland Park and University Park. Dallas, Fort Worth and Southlake each post their own code pages. Codes can change, so confirm with the city before you finalize glass.

What do real product ratings look like?

Ratings vary by product type, glass and grid. Jada publishes a sample on its energy page. In its first glass column, an outswing window rates a U-factor of 0.37 and an SHGC of 0.28. A direct-set fixed window rates 0.31 and 0.32.

The table below repeats Jada’s published sample for its four glass and grid columns. Jada calls them a “sampling.” They are not a quote for your project.

Jada sample	Clr-NG (U / SHGC)	Clr-SDL (U / SHGC)	IS20-NG (U / SHGC)	IS20-SDL (U / SHGC)
Direct-set fixed	0.31 / 0.32	0.34 / 0.29	0.26 / 0.32	0.28 / 0.29
Outswing window	0.37 / 0.28	0.40 / 0.26	0.33 / 0.27	0.35 / 0.25
Outswing door	0.33 / 0.31	0.36 / 0.28	0.29 / 0.31	0.31 / 0.27
Folding door	0.34 / 0.32	0.35 / 0.28	0.30 / 0.31	0.32 / 0.27
Sliding door	0.37 / 0.32	0.39 / 0.29	0.32 / 0.31	0.35 / 0.28

Two points stand out. First, the IS20 glass column shows lower U-factors than the clear column for every product. Second, the lowest SHGC in the sample is 0.25, for the outswing window with IS20 glass and simulated divided lites. A figure of exactly 0.25 is not “under 0.25.”

That does not mean steel cannot meet a target. It means the sample glass is one choice among several, and a project aiming for a low SHGC needs a glass package chosen for it. Ask the maker for ratings with the lowest-SHGC glass it offers. Jada’s glazing page says glass makeups can combine “thermal reduction, as well as, tint controls, UV blocking and sound inhibition.”

Does the frame change the number?

Yes. The frame is part of the whole-window rating. Metal frames conduct heat, so they need a thermal break. The Department of Energy says: “If the frame or sash component is mostly metal, it needs to have carefully integrated thermal breaks to minimize conductive heat flow.”

Doors are different from windows. ENERGY STAR notes that even doors with lots of glass have a lower glass-to-frame ratio than windows, so doors can add more insulation. In a big opening, the glass is still the main factor, and the frame trims what the glass delivers.

Jada notes that muntin style matters too. Its page says simulated divided lites “rate better because the divided lite elements do not break up the glass.” If you want the look of true divided lites, ask for the rating with that exact grid before you commit.

For frame types, see the frame comparison guide.

How far apart are a weak window and a strong one?

The gap is large. The Department of Energy compares three cases in a federal purchasing table. A less efficient model is a double-pane clear window with a U-value of 0.47 and an SHGC of 0.7. The most efficient model is a triple-pane, low-e, argon window with a U-value of 0.12 and an SHGC of 0.21.

That most efficient model comes from a Minneapolis design guide. It is a cold-climate case with a low visible transmittance, so it is not a Texas target. It does show the range. Old clear glass lets in most of the sun’s heat. A well-built unit lets in a small share.

The same page makes a cost point for federal buyers. It says ENERGY STAR-qualified windows “save money if priced no more than $2/ft2 (in 2020 dollars) above less efficient models.” That is a federal acquisition calculation, not a quote for your home. Use it as a reminder to compare lifetime energy cost, not only the purchase price.

What else cuts heat besides the window?

Shade works, and it costs less than glass. The Department of Energy says “exterior overhangs or sunscreens and interior blinds or shades can also be used to effectively reduce undesirable solar heat gain.” Plan roof overhangs, porches and pergolas with the glass.

The Department of Energy also warns about tint. It says “tinting can reduce solar heat gain” but “it also reduces the ability to see clearly through a glazing unit,” and therefore does not recommend it for residential buildings. A spectrally selective low-E coating cuts heat “without significantly impacting visible light or color,” in the Department’s words.

Good installation matters as well. A tight seal around the frame keeps air from bypassing the rating. See the low-E coating entry and the glass options guide.

Is there still a federal credit for windows?

No. The IRS says: “You can claim the credit for improvements made through December 31, 2025.” That date has passed. Do not count on the federal energy efficient home improvement credit for windows bought now.

Utility programs change from year to year. Ask your utility and your builder what is current. This guide does not list a rebate it has not confirmed.

How do I turn all this into a spec?

Start with your target, then ask for ratings. Write the target as a short line, such as “whole-window SHGC and U-factor at or below the figures for our zone and our city’s code.” Then collect ratings for each opening type.

1. Find your ENERGY STAR climate zone for your address.
2. Ask your city’s permit office which energy code year applies.
3. List each opening type: fixed, casement, door, slider, fold.
4. Request NFRC U-factor, SHGC and VT for each type with your glass and grid.
5. Confirm the figures are whole-unit, not center-of-glass.
6. Plan shade for the west and south walls.
7. Keep the rating sheets with your permit file.

Next step

Honey Rock Window and Door can walk you through glass choices for each wall of your home. Start on the energy-efficient windows page, then use Start your project or call (214) 484-9982.